1. Field of the Invention
The present invention provides a method for producing homo- and co-polymers of ethylene, or more particularly a method for producing homo- and copolymers of ethylene by using a catalyst with high activity to produce said polymers with high bulk density and narrow molecular weight distributions.
2. Description of the Related Art
Catalysts containing magnesium for polymerization or copolymerization of ethylene are known to have very high catalytic activities and to produce polymers with high bulk density and are suitable for use in liquid phase or gas phase polymerizations. Liquid phase polymerization of ethylene denotes a polymerization process performed in a medium such as bulk ethylene, isopentane, or hexane. Important characteristics of catalysts used in this process include high catalytic activity, production of a reasonable bulk density of the resultant polymers, etc. Of these characteristics, catalytic activity is deemed to be the most important.
Many titanium-based catalysts containing magnesium for olefin polymerization, and the manufacturing methods thereof have been reported. Many processes that use magnesium solutions to produce catalysts capable of generating olefin polymers with a high apparent bulk density are known. A magnesium solution may be obtained by reacting magnesium compounds with electron donors such as alcohols, amines, cyclic ethers, or organic carboxylic acids in the presence of a hydrocarbon solvent. The use of an alcohol as an electron donor is disclosed in U.S. Pat. Nos. 4,330,649 and 5,106,807. Further, methods for the production of catalysts containing magnesium by reacting a liquid-phase magnesium solution with a halogenated compound such as titanium tetrachloride are well known. Moreover, there have been attempts to control polymerization activity or molecular weight distribution by adding ester compounds. Such catalysts produce polymers with a high bulk density; however, improvements can still be made with respect to catalytic activity and molecular weight distribution of the resulting polymers. Moreover, tetrahydrofuran, a cyclic ester, has been used as a solvent for magnesium compounds in U.S. Pat. Nos. 4,477,639 and 4,518,706.
U.S. Pat. Nos. 4,847,227, 4,816,433, 4,829,037, 4,970,186, and 5,130,284 have reported the use of electron donors such as dialkylphthalate, phthaloyl chloride, etc. in reactions with a titanium chloride compound in the production of olefin polymerization catalysts. These catalysts display superior polymerization activity and are also capable of enhancing the bulk density of the resulting polymers.
U.S. Pat. No. 5,459,116 teaches a method of production of a titanium solid catalyst by contact-reacting a magnesium solution containing an ester having at least one hydroxyl group as an electron donor with a titanium compound. By this method, it is possible to obtain a catalyst with high polymerization activity, which also produces high bulk density to the resulting polymers; however, there is still room for further improvement.
With respect to polymerization of α-olefins, particularly, with respect to polymerization of propylene, the art of using external electron donors for increasing stereo-regularity is commonly known in the field and is widely used in the industry. As for external electron donors, alkoxy silane compounds are widely known. However, in these cases, the stereo-regularity of polymers increases, but the molecular weight distribution broadens in relative terms. Korean Patent Notification No. 93-665 discloses a method of broadening the molecular weight distribution by using an organic silane as an external electron donor during polymerization of propylene, and the benefits thereof.